The burden of unmet mental health and substance use need and HIV risk among youths in the juvenile justice system is alarmingly high. A behavioral Continuum of Care approach, emphasizing coordination of services across multiple sectors of care, has promise for addressing unmet needs across these domains. Although evidence-based practices (EBPs) for identification, referral, and treatment of behavioral health problems in justice-involved youths exist, they are rarely implemented in routine practice. Based on our prior success in NYS juvenile probations, our expertise uniquely positions us to address identification and linkage, which initiates the operation of the behavioral health continuum. Compared to standard care, our earlier efforts boosted POs' use of targeted linkage practices that related, in turn, to increased service access. Here (Connect Plus) we expand earlier efforts to address substance use and HIV risk (via screening, referral practices, and interagency collaboration). We propose a multi-stakeholder Research Center to promote EBPs addressing challenges in juvenile probationers' linkage to behavioral health services. We are guided by the Comprehensive Framework for Implementation Research (CFIR) to support acceptability, feasibility, and sustainability. To accomplish Aim 1 (Baseline), we plan to measure current system capacity in 4 NY counties to (a) identify behavioral health needs and HIV risks in justice-involved youths, and (b) link identified youths to appropriate services. Reviewing what is learned from Aim 1 activities will likely identify service gaps. To accomplish Aim 2 (Connect Plus Implementation), we will build upon Aim 1 findings to implement a Continuum of Care approach to delivery of behavioral health care in the same counties. Implementing the Continuum approach will likely require enhancing procedures for both identification and linkage across service sectors. We adapt those activities and employ CFIR-informed change process components that include an interlocking set of meeting venues, Quality Assurance activities and a Learning Collaborative to set goals, monitor progress, and address identified barriers, thereby promoting uptake of Connect Plus elements. We are guided by a Learning Collaborative (Research Partners and representatives from NY state and county juvenile probation, mental health, and substance use service agencies) to design and interpret Aim 1 assessments, manage implementation of Aim 2 activities, interpret findings, and promote sustainability and dissemination in other settings. All proposed project activities will be cooperatively defined and implemented in full collaboration with our Service Partners and the wider TRIALS Cooperative. Innovative components include modifying the statewide probation case management software that electronically records case management decisions to capture information on probation practices and youth characteristics. We build upon work supporting structured handoff protocols in managing patient service transitions, which is likely to reduce both adverse events and service gaps. Finally, we use a state-of-the-art distance-learning platform, to promote intervention scalability.